Allah T'ala says in the Holy Quran:
إِنَّ اللّهَ يَأْمُرُكُمْ أَن تُؤدُّواْ الأَمَانَاتِ إِلَى أَهْلِهَا وَإِذَا حَكَمْتُم بَيْنَ النَّاسِ أَن تَحْكُمُواْ بِالْعَدْلِ إِنَّ اللّهَ نِعِمَّا يَعِظُكُم بِهِ إِنَّ اللّهَ كَانَ سَمِيعًا بَصِيرًا
(4:58) Allah commands you to deliver trusts to those worthy of them; and when you judge between people, to judge with justice. Excellent is the admonition Allah gives you. Allah is All-Hearing, All-Seeing.
Degenration of a nation comes when religious and political leadership, positions of trust, are handed over to incompetent, mean, immoral, dishonest and corrupt people. This results into the spread of corruption throughout the nation. The Muslims are directed to take heed of this, and to entrust positions of responsibility only to those who are capable of shouldering the burdens of such positions.
The other major weakness of a nation is loss of sense of justice. In their pursuit of either personal or national interests, honesty and good faith are often sacrificed. Allah T'ala has warned Muslims against committing injustices. They should do what is right in the face of friend and foe alike, and judge between people with equity and justice.